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GEOLOGY 12
CHAPTERS 20 + 21
MINERAL AND ENERGY RESOURCES
QUESTIONS FOR REVIEW
ANSWERS
CHAPTER 20 MINERAL RESOURCES
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What is the distinction between reserves and resources? Under what conditions
might some resources be reclassified as reserves?
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Reserves are the quantity of a mineral (or fuel) that has been found and
identified, and can be exploited economically with existing technology.
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Resources include reserves, plus undiscovered deposits expected to be found,
plus known deposits that are uneconomic. If demand rises and prices rise in
response, some deposits that had been uneconomic may become economic,
and justify reclassification as reserves.
What is an ore? How is its concentration factor defined?
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An ore is a rock in which an economically valuable or useful metal is
concentrated beyond its average crustal concentration to such an extent that it
is profitable to mine.
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The concentration factor is the ratio of the metal concentration in the ore to its
average concentration in the crust.
Describe two kinds of magmatic ore deposits, and name one mineral mined from
each. (Several answers are possible.)
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Kimberlite pipes are sources of diamonds. Chromite, magnetite, and other metal
ores may be concentrated by gravitational settling in a magma chamber.
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Pegmatites may yield large crystals of uncommon minerals like beryl,
tourmaline, and others, some of which also concentrate rare metals.
What are hydrothermal ore deposits? Why are they especially associated with
plate boundaries?
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Hydrothermal ore deposits are deposits precipitated from warm, metal-rich
fluids circulating through rocks. The fluids, and sometimes the metals, may be
derived from magmas; magmas also supply the heat.
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Because magmatic activity is particularly concentrated at plate boundaries;
hydrothermal ore deposits are also concentrated there.
Under what conditions do evaporites form?
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Evaporites form when seawater in a restricted basin dries up. Multiple basins
full of water may be needed to make a thick deposit.
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One setting in which suitable conditions may develop is during the early stages
of continental rifting.
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What is a placer deposit, and what kinds of minerals are concentrated in these?
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Placers are sedimentary deposits in which dense and/or resistant minerals are
concentrated by stream action and sediment sorting.
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Diamonds, gold, and cassiterite (tin oxide) are among minerals concentrated in
this way.
Name and describe two kinds of exploration techniques used in the search for
mineral deposits.
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Magnetic anomalies may be used to localize deposits of magnetic minerals,
especially iron ores.
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Radioactivity surveys can locate uranium ores.
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Geochemical prospecting for selected elements may find ores of those
elements through enrichment in soil or plant materials.
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Remote sensing lets us scan broad areas for anomalous features that may
indicate ore deposits below.
How has the development of plate-tectonic theory aided in finding more ore
deposits?
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The association of magmatic activity and hydrothermal ores with plate
boundaries has focused our search for the corresponding ores on those
boundaries.
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Also, we can now project from known deposits at the edge of one plate to the
corresponding edge of another plate.
Is seawater a potential source of essential metals? Explain.
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No. While virtually every known element is found dissolved in seawater at some
concentration, most are too dilute to recover economically.
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Moreover, we do not have efficient technology to separate, selectively,
individual trace elements from seawater and its more abundant components
(sodium, chloride, calcium, etc.).
Geology 12
Chapters 20 & 21
Questions For Review
Page 2
DISCUSSION NOTE:
12.
Why are some old mines and tailings piles being considered as future metal
sources?
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13.
Some lower-grade ore is typically left unmined, and some ore is left in tailings
even after processing. As demand and prices rise, it becomes economic to go
back and rework these lower-grade materials.
Describe one potential environmental problem or hazard associated with (a)
underground mining; (b) surface mining; and (c) mineral processing after mining
(tailings).
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Underground mines may cave in and the land above them collapse as support
timbers rot or soluble rocks dissolve away,
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Surface mining may leave unsightly spoils and/or exposed rock. This is
susceptible to accelerated weathering, which may release toxic elements into
surface water or groundwater.
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Tailings left after processing may also weather easily, and fine tailings may
further be washed away causing sediment pollution of surface runoff.
Geology 12
Chapters 20 & 21
Questions For Review
Page 3
CHAPTER 21 ENERGY RESOURCES
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What are the two basic initial requirements for forming a fossil fuel deposit?
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Accumulation of large amounts of organic matter.
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Rapid burial to protect it from decomposition by reaction with oxygen.
Briefly outline the process of petroleum formation and maturation.
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With moderate heat and pressure, complex organic molecules break down, first
into long-chain polymers (heavy hydrocarbons), and then progressively into
smaller and smaller molecules (lighter hydrocarbons).
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The end product of this process is methane (CH4).
Sketch or describe any two types of petroleum traps.
(Sketches omitted.)
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Oil can be trapped in a porous reef within impermeable rocks
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Anticline (antiform) capped by impermeable rocks.
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Permeable strata overlain by impermeable ones that abut an impermeable salt
dome.
What is geopressurized natural gas, and where is it found?
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Geopressurized natural gas is gas dissolved in pore waters under high
pressure.
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It is found deep in the crust, at depths below which oil has been completely
broken down in response to the high temperatures.
From what materials is coal formed? How does its quality change with progressive
heating?
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Coal is formed from land plants. Up to a point, progressive heating makes it
more compact, harder, and more carbon-rich, producing a corresponding
increase in weight burned.
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Too much heating, however, may cause coal to be converted to graphite, which
is not useful as fuel.
What is oil shale? How is fuel produced from it?
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Oil shale is a sedimentary rock containing the waxy solid hydrocarbon
KEROGEN.
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It must be mined, crushed, and heated to extract the hydrocarbon, which can
then be distilled into "shale oil."
Geology 12
Chapters 20 & 21
Questions For Review
Page 4
11.
Cite three environmental or developmental problems associated with both oil shale
and tar sand.
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A lot of water is required in the processing
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Water may become polluted.
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Waste rock to dispose of greater than the original volume of rock mined.
DISCUSSION NOTE:
8.
Name and describe one environmental problem associated with coal mining and
coal use/burning.
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Underground mining carries with it the potential for mine collapse, mine fires,
and acid drainage.
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Strip-mining may involve acid runoff and sediment pollution before reclamation
is completed.
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Coal burning adds CO2 to the air, as is the case with all fossil fuels.
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Burning also adds sulfur gases that produce sulfuric acid by reaction with air
and water, which contributes to acid rain.
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Much waste ash is also produced, which requires proper disposal.
Geology 12
Chapters 20 & 21
Questions For Review
Page 5